In patients with hemophilia, intravenous administration of blood coagulation factors, e.g., factor VIII, is a safe and effective therapeutic approach for the treatment and prevention of bleeding episodes. However, up to 30% of the patients receiving factor VIII treatment develop an inhibitory immune response to the administered factor VIII such that subsequent treatment is no longer effective. For those inhibitor patients whose immune response cannot be suppressed, so-called inhibitor by-passing agents, e.g. recombinant human factor VIIa (rFVIIa), are used to treat bleeding episodes. To treat a severe bleeding episode with currently available by- passing agents requires multiple intravenous doses. Development of a by-passing agent with longer duration of effect such that fewer injections are required would be a major advance in therapy. The goal of the current application is to evaluate a novel bioengineered protein (Chimera) that consists of functionally important structural domains of blood coagulation factor IX (FIX) that replace the homologous domains of rFVIIa. In preliminary studies the Chimera has been found to be as effective as rFVIIa in treating bleeding in an animal model of hemophilia. The Chimera also displays a dramatically reduced thrombotic potential. The hypothesis of this application is that the Chimera will have an extended half-life of therapeutic effectiveness. The FIX structural properties of the Chimera are anticipated to reduce clearance by natural inhibitors. This is anticipated to increase the plasma half-life. Further, the FIX structural properties are expected to substantially increase distribution of the protein into the extravascular space where it is anticipated to persist in an active form even after plasma levels have returned to baseline. In the current application we propose to utilize readily available commercial technology to manufacture sufficient amounts of the Chimera to rigorously evaluate the structural and functional properties of the protein. Well characterized protein will be advanced to in vivo evaluation of the circulating half-life and prolonged hemostatic effectiveness in a well-established mouse model of bleeding in hemophilia. We anticipate that the proposed work will show a significant increase in the circulating half-life of the Chimera relative to rFVIIa. We also anticipate that hemostasis will be maintained in a bleeding model for even longer than the circulating half-life. Such results will suggest that it could be plausible for prophylactic dosing with the Chimera to be extended from daily to at most once every second day with the possibility of once weekly dosing while achieving breakthrough bleeding rates comparable to what has been observed with replacement therapy. This significant increase in effectiveness would warrant further commercial development of the chimera product under a Phase II SBIR application wherein cell line development would begin in order to produce representative clinical product for evaluation in the dog model of hemophilia. This canine model has been documented to correlate well with the clinical effectiveness of hemophilia products in humans.